1. Field of the Invention
This invention relates to a process for simultaneously deasphalting and extracting an asphalt containing mineral oil and recovering the extraction solvent. More specifically, this invention is a process for simultaneous solvent deasphalting and extracting a mineral oil containing asphaltic and aromatic components in a combination zone which comprises contacting said oil with a solvent comprising a mixture of a light hydrocarbon and N-methyl-2-pyrrolidone (hereinafter referred to as NMP for the sake of brevity) to produce raffinate and extract phases, separating the solvent from the raffinate phase and recycling the separated solvent back to the combination zone. Still more particularly, the present invention is a process for simultaneously solvent deasphalting and extracting a petroleum oil containing asphaltic and aromatic components which comprises contacting the oil, in a combination zone, with a solvent comprising a mixture of (a) at least one liquid, low molecular weight C.sub.2 -C.sub.10 carbon atom hydrocarbons and (b) NMP containing from about 0-5 LV% water to produce raffinate and extract phases with the raffinate phase containing the desired oil, most of the hydrocarbon solvent and some NMP, heating the solvent containing raffinate to flash off most of the hydrocarbon solvent therefrom followed by chilling the hydrocarbon solvent reduced raffinate to produce bulk liquid-liquid immiscibility between the NMP and the raffinate oil, separating the NMP from the oil and recycling the NMP back into the combination zone.
2. Description of the Prior Art
It is well known to those skilled in the art to deasphalt asphalt-containing mineral oils with light or low molecular weight hydrocarbons such as propane, especially in the preparation of lubricating oils from resids and crude oils. In such a process, an oil feedstock or stream containing asphaltic type constituents is mixed with a light hydrocarbon, such as liquid propane, under temperature and pressure conditions whereby the asphaltic type constituents are precipitated. After separation of the asphaltic type constituents from the deasphalted oil, the respective streams are handled in well known manners in order to recover the solvent. It is also well known to those skilled in the art to treat certain types of oil feedstocks, particularly distillate lube oil feedstocks, with various solvents in order to separate the relatively more aromatic and polar type constituents having low VI, from the relatively more paraffinic type constituents having high VI. The more commonly employed extraction solvents useful in such processes include phenol, various cresols, furfural, sulfur dioxide, and more recently, solvents such as NMP along with minor amounts of water. In such extraction operations the oil is contacted with a solvent such as phenol, containing minor amounts of water, either in a countercurrent treating operation or in a multistage batch operation under temperature and pressure conditions designed to secure phase separation. As a matter of practice, the oil to be treated is usually introduced into one end of a countercurrent treating zone while a solvent or solvent mixture is introduced at the other end. The solvent and oil flow countercurrently under temperature and pressure conditions to produce a raffinate phase and an extract phase. The solvent rich extract phase is withdrawn from one end of the countercurrent treating zone and contains most of the aromatic and polar components of relatively low VI, while the oily or solvent poor raffinate phase, containing the more paraffinic, high VI type constituents is withdrawn from the other end of the treating zone. The respective streams are then handled in well known manners to separate and recover the solvent.
Another process well known to those skilled in the art is the Duo-Sol process for the extraction of high VI, light color, low carbon residue lube base stocks from either residual or distillate lube feeds. This is a simultaneous deasphalting-extraction process which derives its name from the use of two solvents. The solvents employed are propane and a blend of cresol and phenol. The propane preferentially dissolves a relatively high VI, paraffinic type of lube base stock from the feed, while the cresol and phenol preferentially dissolve the asphalt, undesirable aromatics, polars and color bodies from same as an extract. The combination lube process disclosed in U.S. Pat. No. 3,291,718 incorporates a Duo-Sol extraction deasphalting operation, wherein a suitable feed such as an atmospheric resid is fed into the middle of a deasphalting-extraction zone, while propane is fed into the bottom and phenol is fed into the top to produce a deasphalted raffinate phase relatively low in aromatics and polars and from which useful, high VI lube oils are made. NMP has recently been suggested as useful for deasphalting and for simultaneous deasphalting-solvent refining. In U.S. Pat. No. 3,779,895, NMP is suggested as being a member of a group of solvents consisting of low molecular weight paraffins containing 3-10 carbon atoms, NMP and furfural, for deasphalting aqueous dispersions of heavy petroleum fractions which have been pretreated with high temperature steam. Finally, in U.S. Pat. Nos. 3,779,896 and 3,816,295, lube oils are prepared by subjecting a residuum-containing petroleum fraction to simultaneous deasphalting-solvent refining using either furfural or NMP as the combination deasphalting-solvent refining solvent and most preferably NMP, because of its greater thermal stability and solvent capacity.
Therefore, because the disclosures in the prior art have not suggested using a combination of NMP and light hydrocarbon solvents for simultaneously deasphalting and extracting an asphalt-containing oil, it was not known whether or not such a system would work. Hence, when it was found that this system would work, U.S. patent application Ser. No. 683,376 (now abandoned) was filed claiming such a process. However, it was further discovered that the raffinate produced by this process contained excessive amounts of NMP which meant that a method had to be found for separating the NMP from the raffinate phase and recycling the NMP back into the combination deasphalting-extracting zone in order to make the combination process economically viable.